1. Field of the Invention
The present invention relates to a novel optically active naphthalene derivative useful as the component of a ferroelectric liquid crystal composition, process for preparation thereof, liquid crystal composition containing the same as an effective component, and liquid crystal element using the same.
2. Prior Art
Liquid crystal display elements currently in the most wide use are of the TN (twisted nematic) type display system. The TN liquid crystal display has a number of advantages including low operating voltage and low power consumption. In point of the speed of response, however, they are inferior to light-emitting type display elements such as cathode-ray tubes, electroluminescence, plasma display, etc. Although a new TN type display element in which the twisted angle was made to 180.degree.-270.degree. has been developed, its speed of response is still not sufficiently high. Thus, in spite of various efforts for improvement, a TN type display element with a high speed response has not come into a reality yet. However, in a new display system which uses ferroelectric liquid crystals and which has been extensively studied in recent years, there is a possibility of improving the speed of response markedly (Clark et al., Applid. Phys. Lett., 36, 899 (1980)). This system makes use of chiral smectic phases which show ferroelectricity, such as the chiral smectic C phase (hereinafter abbreviated as Sc*). It is known that ferroelectricity is exhibited not only by Sc* phase but also by the chiral smectic phases F, G, H, I, etc.
Ferroelectric liquid crystal materials for use in ferroelectric liquid crystal elements used in practice are required to have a number of characteristics. At the present time, no single compound is able to meet all these requirements; it is necessary to use ferroelectric liquid crystal compositions obtained by mixing several liquid crystal compounds or non-liquid crystal compounds.
Apart from ferroelectric liquid crystal compositions comprising ferroelectric liquid crystal compounds alone, Japanese Patent Application Kokai No. 61-195187 discloses that a compound and/or composition which assumes the phase of non-chiral smectic C, F, G, H, I etc. (hereinafter abbreviated as "phase of Sc etc.") is used as the basic material and one or more compounds which assume a ferroelectric liquid crystal phase are mixed therewith to obtain the whole as a ferroelectric liquid crystal composition. Further, it has been reported that a compound and/or composition which assumes the phase of Sc etc. is used as-the basic material and is mixed with one or more compounds which, though optically active, do not assume a ferroelectric liquid crystal phase, to obtain the whole as a ferroelectric liquid crystal composition (Mol. Cryst. Liq. Cryst., 89, 327 (1982)).
Considering the above-mentioned information, it is recognized that ferroelectric liquid crystal compositions can be composed by using one or more optically active compounds as the basic material irrespective of whether the compounds assume a ferroelectric liquid crystal phase or not. However, it is preferable that the optically active substance desirably assumes a liquid crystal phase and that, even when it assumes no crystal liquid phase, it is similar in structure to a liquid crystal compound, namely it is, so to speak, a quasi-liquid crystal substance. However, no liquid crystal material has been found up to the present time which has spontaneous polarization necessary for high speed response, has low viscosity and assumes a ferroelectric liquid crystal phase over a wide temperature range including the region of room temperature.